Add IRPGO and CSIRPGO options to Swift #84335

chiragramani · 2025-09-17T00:01:56Z

This PR introduces three new instrumentation flags and plumbs them through to IRGen:

-ir-profile-generate - enable IR-level instrumentation.
-cs-profile-generate - enable context-sensitive IR-level instrumentation.
-ir-profile-use - IR-level PGO input profdata file to enable profile-guided optimization (both IRPGO and CSIRPGO)

Context: https://forums.swift.org/t/ir-level-pgo-instrumentation-in-swift/82123

Swift-driver PR: swiftlang/swift-driver#1992

Tests and validation:
This PR includes ir level verification tests, also checks few edge-cases when -ir-profile-use supplied profile is either missing or is an invalid IR profile.

However, for argument validation, linking, and generating IR profiles that can later be consumed by -cs-profile-generate, I’ll need corresponding swift-driver changes. Those changes are being tracked in swiftlang/swift-driver#1992

The plan is:

Land this PR first.
Then update swift-driver with the required changes.
Then add the remaining set of test cases in this repo.

~~Open Questions (Reviewer Input Requested)~~

1. Naming:
Is -ir-profile-generate a good flag name?
-cs-profile-generate pairs nicely with Clang’s -fcs-profile-generate. However, -ir-profile-generate feels closer to Clang's -fprofile-generate but -profile-generate already exists in Swift as a frontend level and not IR level. Should it stay as is, or is there a clearer alternative?

2. Missing LLVM runtime + Blocked on tests

At the moment, I haven’t added tests because they currently fail locally due to missing LLVM runtime symbols. This is expected, since the required runtime linking through libclang APIs will be handled in swift-driver(swiftlang/swift-driver#1992). However, swift-driver itself depends on these new options being available in Swift.

~~Does that mean the correct order of the PRs should be the following?~~

1. Create a PR in Swift that introduces just the new options, and land that PR first.
2. Land the corresponding swift-driver PR to handle runtime linking,
3. Then follow up with a Swift PR adding the full functionality and tests?
~~

Updated config

aschwaighofer · 2025-09-17T14:29:19Z

I don't have a strong opinion on naming. My feeling is that context sensitive and non context sensitive LLVM IR level instrumentation should follow a similar pattern to make clear they are related. We have already deviated from clang's naming scheme -- that is, clang's fprofile-generate(llvm ir level instrumentation) is not equal swift's -profile-generate ("AST" based insertion of instrumentation). -ir-profile-generate and -cs-ir-profile-generate would make it clearer that they are related.

aschwaighofer · 2025-09-17T14:53:22Z

Does that mean the correct order of the PRs should be the following?
Create a PR in Swift that introduces just the new options, and land that PR first.
Land the corresponding swift-driver PR to handle runtime linking,
Then follow up with a Swift PR adding the full functionality and tests?

You could add LLVM IR level tests that test the functionality of this PR (look at most tests in test/IRGen) and merge this PR first. Then you could land the corresponding swift-driver PR. Then you could at a swiftlang/swift repo commit to add execution tests.

// RUN: %target-swift-frontend -ir-profile-generate -emit-ir %s | %FileCheck %s

// CHECK: define @mangleNameOfA
// CHECK: the llvm ir you expect to see (calls to profile runtime function/intrinsics)
public func a(_ cond: Bool) {
  if cond {
     b()
  } else {
    c()
  }
}

Preferably, you would as .sil tests rather than .swift tests as that would make them more "stable".

That would look something like the following (I ran swiftc -emit-sil test.swift and edited the output a little bit):

// RUN: %target-swift-frontend -ir-profile-generate -emit-ir %s | %FileCheck %s

sil_stage canonical

import Builtin
import Swift
import SwiftShims

sil @b : $@convention(thin) () -> ()

sil @c : $@convention(thin) () -> ()

// CHECK: define {{.*}} void @a
// CHECK: the llvm ir you expect to see (calls to profile runtime function/intrinsics)

sil @a : $@convention(thin) (Bool) -> () {
bb0(%0 : $Bool):
  %2 = struct_extract %0, #Bool._value
  cond_br %2, bb1, bb2

bb1:
  // function_ref b()
  %4 = function_ref @b : $@convention(thin) () -> ()
  %5 = apply %4() : $@convention(thin) () -> ()
  br bb3 

bb2:
  // function_ref c()
  %7 = function_ref @c: $@convention(thin) () -> ()
  %8 = apply %7() : $@convention(thin) () -> ()
  br bb3 

bb3:
  %10 = tuple ()
  return %10
}

lib/IRGen/IRGen.cpp

chiragramani · 2025-09-18T02:17:12Z

Preferably, you would as .sil tests rather than .swift tests as that would make them more "stable".

You could add LLVM IR level tests that test the functionality of this PR (look at most tests in test/IRGen) and merge this PR first. Then you could land the corresponding swift-driver PR. Then you could at a swiftlang/swift repo commit to add execution tests.

Thanks for the guidance here, it definitely helped me understand things better!

Added tests

Option dedicated for IR level PGO uses

chiragramani · 2025-09-19T17:30:29Z

Hi @aschwaighofer, I've added the tests based on your suggestions. When you have a moment, could you please review the changes and share your feedback? Thanks

include/swift/Option/Options.td

test/IRGen/cs_profile_generate.sil

chiragramani · 2025-09-22T20:15:09Z

@kavon would love to hear your perspective on this PR as well, when you have a moment.

chiragramani · 2025-09-22T20:58:30Z

@swift-ci test

chiragramani · 2025-09-25T20:16:25Z

Hey @aschwaighofer, would it be possible for you to tag or add the respective POCs who could help review this PR please? I’d really appreciate it.

drodriguez · 2025-09-25T21:46:10Z

@swift-ci please test

chiragramani · 2025-09-30T19:34:57Z

@swift-ci please test

drodriguez · 2025-10-01T00:08:28Z

@swift-ci please test

drodriguez · 2025-10-01T00:10:53Z

please test

@chiragramani sadly you need a special role for starting the tests. The details are in https://www.swift.org/contributing/#member (still some hoops to jump through, but easier than before)

aschwaighofer · 2025-10-01T14:20:18Z

@swift-ci test

aschwaighofer

LGTM

drodriguez · 2025-10-01T18:11:40Z

@swift-ci please test

chiragramani · 2025-10-01T19:18:53Z

@chiragramani sadly you need a special role for starting the tests. The details are in https://www.swift.org/contributing/#member (still some hoops to jump through, but easier than before)

Really appreciate you helping trigger the tests and sharing the process. I’ll send in a request soon.

…onventions

aschwaighofer · 2025-10-02T16:47:12Z

@swift-ci please test

chiragramani · 2025-10-02T23:56:51Z

Swift Test Linux Platform — Failed

I noticed that the above job has failed, but I’m unable to open the link for the Linux job details. Could someone with access kindly share the logs or error message? Thanks

drodriguez · 2025-10-03T01:54:37Z

ci.swift.org seems to give me time-outs. It might be having a bad day.

chiragramani · 2025-10-03T21:05:14Z

ci.swift.org seems to give me time-outs. It might be having a bad day.

Thanks for checking. It looks like the link works now, but the error seems related to a CI infra issue (agent removal). Would it be possible to retry the job?

drodriguez · 2025-10-03T21:24:23Z

@swift-ci please test Linux platform

chiragramani · 2025-10-08T21:17:29Z

@swift-ci please test Linux platform

Thanks! The smoke test ran post this but the Swift Test Linux Platform didn’t get picked up. Can we give it another run/retry please 🙏?

drodriguez · 2025-10-08T21:21:30Z

The "(smoke test)" gets fulfilled by the non smoke test. It seems, however, that your comment quote did trigger the Linux Platform build in https://ci.swift.org/job/swift-PR-Linux/24357/ so I cannot check the previous results, but hopefully those will turn green.

(I have a couple of PRs and I am also in testing hell, but in my case with macOS failing randomly all the time… patience)

chiragramani · 2025-10-08T23:00:33Z

******************** TEST 'Swift(linux-x86_64) :: Interop/Cxx/class/access/swiftify-private-fileid.swift' FAILED ********************
15:30:00  couldn't parse text: '://162106643'
15:30:00  in expression: 'rdar://162106643'
15:30:00  in REQUIRES: directive on test line 1
15:30:00  ********************

It failed 😅
I saw that the failure is in swiftify-private-fileid.swift, but it looks unrelated to this PR changes. Any suggestions how to go about it?

drodriguez · 2025-10-08T23:47:05Z

#84775 should take care of those. It has been one of those weeks.

drodriguez · 2025-10-08T23:47:16Z

@swift-ci please test Linux platform

chiragramani · 2025-10-09T19:49:11Z

Thank you for all your help @drodriguez , its all green now 🙌

This PR introduces three new instrumentation flags and plumbs them through to IRGen: 1. `-ir-profile-generate` - enable IR-level instrumentation. 2. `-cs-profile-generate` - enable context-sensitive IR-level instrumentation. 3. `-ir-profile-use` - IR-level PGO input profdata file to enable profile-guided optimization (both IRPGO and CSIRPGO) **Context:** https://forums.swift.org/t/ir-level-pgo-instrumentation-in-swift/82123 **Swift-driver PR:** swiftlang/swift-driver#1992 **Tests and validation:** This PR includes ir level verification tests, also checks few edge-cases when `-ir-profile-use` supplied profile is either missing or is an invalid IR profile. However, for argument validation, linking, and generating IR profiles that can later be consumed by -cs-profile-generate, I’ll need corresponding swift-driver changes. Those changes are being tracked in swiftlang/swift-driver#1992

Add IRPGO and CSIRPGO options to Swift

08bc2e1

Updated config

chiragramani mentioned this pull request Sep 17, 2025

Adds IR level PGO Instrumentation options swiftlang/swift-driver#1992

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ellishg reviewed Sep 17, 2025

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Address suggestions

fb55618

Added tests

chiragramani force-pushed the ir_options branch from f5c8119 to fb55618 Compare September 18, 2025 02:37

chiragramani added 2 commits September 17, 2025 20:35

Adds ir_profile_use

7a01d0c

Option dedicated for IR level PGO uses

Add supporting for remaining UseIRProfile cases

83f4c14

chiragramani force-pushed the ir_options branch from 2c32821 to 83f4c14 Compare September 18, 2025 05:23

Add tests for -ir-profile-use

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chiragramani marked this pull request as ready for review September 18, 2025 18:44

chiragramani requested review from AnthonyLatsis, artemcm, hborla, rjmccall, slavapestov, tshortli and xedin as code owners September 18, 2025 18:44

ellishg reviewed Sep 19, 2025

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Address suggestions and relax IR checks

a96b390

chiragramani requested a review from ellishg September 22, 2025 19:32

Relax IR checks

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aschwaighofer reviewed Oct 1, 2025

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aschwaighofer approved these changes Oct 1, 2025

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Make LLVM passes check order independent

35b7c75

Ignore case for error message as different platforms have different c…

9dc6932

…onventions

drodriguez merged commit 5179bc9 into swiftlang:main Oct 10, 2025
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Add IRPGO and CSIRPGO options to Swift #84335

Add IRPGO and CSIRPGO options to Swift #84335

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